Camera sensors are used when using digital cameras to take individual images or a video image. The sensor image can use various image formats, for example RGB8:8:8, is RGB5:6:5, YUV4:2:0, and a raw-Bayer image. When the image is displayed in the view-finder (VF), which usually has a lower resolution than the image sensor, the image must be formed in the sensor and scaled to a suitable resolution for the display. Images can also be zoomed (a smaller image is delimited from the image and then scaled) to the viewfinder. In zooming, there must be many steps from the full image size towards the larger zooming, so that the result of the zooming will appear to be continuous. When video images are coded, the resolution of the video image is also usually lower than the resolution of the sensor. Thus a similar scaling is also required for video. Camera sensors can also be used equally well in portable devices as in cameras.
Image scaling or modifying the size of digital images has been exploited in several digital image-processing applications. The basic method in image scaling is to arrange a two-dimensionally sampled signal in a new sampling array.
A few possibilities for carrying out image sub-sampling are known from the literature on signal and image processing. The sampling of the signal is essential part in the theory of signal processing and has been widely covered in the literature. Basically, it is a matter of preserving the spectrum of the image below Nyquist frequency.
The general sub-sampling methods include an anti-alias filter and the re-creation of the image from the samples. The sampled data is often got using a linear combination of sampled input data and a specific core.
Sampling algorithms are often compromises between the complexity of the algorithm and the quality of the image obtained.
The simplest form of re-sampling is the ‘nearest neighbourhood’ method. This does not use anti-alias filtering of the original data, but only selects the nearest samples for the new sampling array. The image obtained as a result is thus poor, due to the anti-aliasing effect.
There are many methods for selecting the coefficients for the core of the anti-alias filter.
U.S. Pat. No. 6,205,245 discloses one method, in which a colour image is scaled directly from the sensor's matrix, in such a way that a pixel group, of which one is always processed one at a time, and which corresponds to each pixel of the final image, is defined. In this method, intermediate pixels are jumped over, thus losing original information.